Pretty easy game in my opinion. The only minorly tricky part is the 3rd campaign, but I got around that just be constantly spinning the ball as fast as a could.
nice take on the greek mythology of returning from the underworld with your loved one. only in that version after the hero rescues the girl and escapes the shadow, he turns around too soon as the girl is still in shadow and he loses her forever... pwnt.
The spartan one is by far the easiest :P
You just buy the quaker, max your wall fortifications, buy 3x flame thrower guys and spend the rest on builders. Spam the quake gun and they all die. Done.